Checking device for electrical ignition circuits in internal combustion engines or the like



Aprll 2, 1957 J BENOlT 2,787,726

CHECKING DEVICE FOR ELECTRICAL IGNITION CIRCUITS IN INTERNAL COMBUSTIONENGINES OR THE LIKE Filed Dec. 15. 1953 2 Sheets-Sheet l mmm mve-rmm T3511011 April 2, 1957 .g

CHECKING DEVICE R ELECT BUSTION Filed Dec. 15. 1953 BENOIT 2,787,726ICAL. IGNITION CIRCUITS IN INTERNAL ENGINES OR THE LIKE 2 Sheets-Sheet 2Ff F799 @m mVEHToR: ITEM BEr/o 'r CHECKING DEVICE FOR ELECTRICALIGNITION CIRCUITS 1N INTERNAL COIVBUSTION EN- GINES OR THE LIKE JeanBenoit, Paris, France Application December 15, 1953, Serial No. 398,397

Claims priority, application France December 17, 1952 8 Claims. (Cl.315-22) An object of the present invention is a device allowing theobservation and immediate checking of ignition in an internal combustionengine and of the elements of an electric circuit for such an ignition(coil, spark plug etc.) or any similar circuit.

The device according to the invention consists in an electronic assemblycomprising:

(a) A cathode ray tube.

(b) Means generating for the horizontal scanning a saw tooth voltage theduration of which (scanning time) is constant whatever may be therepetition frequency of the phenomenon.

(0) Means for starting the scanning in synchronism with the pulse to bestudied.

(:1) Means for connecting the pulse to be observed with the verticaldeflection members.

(e) Preferably but not necessarily, means for producing luminosity(suitable excitation of the tube cathode) controlled by the horizontalscanning or the pulse to be studied, in order to avoid a damaging of thescreen by an excessive intensity received at a given point due to theimmobility of the spot in the absence of the pulse to be observed, orbetween two pulses when the latter are separated by an important timeinterval.

The means which can be used for the embodiment of the invention are veryvaried, all kinds of electronic set ups can be adopted. The invention,however, contemplates the following preferred but not limitative set-up.

The horizontal scanning circuit is controlled by two triode tubes (orthe equivalent: two pentode tubes, one double triode tube) assembled ina single equilibrium condition circuit with a change over making itpossible to direct the pulse to be studied to the grid of one or theother tube according to its polarity or any other equivalent arrangementfor this purpose as for instance a rectifier device (such as a doublediode) transmitting pulses of constant polarity, whatever the polarityof the pulses received may be and which device can be connected for thatreason to one only of the two grids.

This circuit is similar to a multi-vibrator circuit in which the timeconstant of one of the equilibrium conditions is made infinite byreplacing a capacity by a resistance and in which voltages of oppositesigns are applied to each grid.

Further, the invention contemplates using the square wave voltage of thecircuit thus obtained for creating the luminosity for the screen by asuitable connectionon the cathode of the cathode ray tube.

There is thus obtained, as will be described hereinafter, with referenceto the appended electrical diagram, by way of an example of embodiment,a saw tooth horizontal scanning voltage, released by the pulse, with aduration which is independent of the repetition frequency of thephenomenon since, according to the invention:

(a) The pulse itself is used as a synchronism signal for the horizontalscanning and only as a signal.

2,787,726 Patented Apr. 2, 1957 ice (b) The scanning time constant isthat defined by its resistance-capacity circuit, i. e. this time isindependent of the frequency of the phenomenon (which is very importantfor the checking of the ignition of an internal combustion engine thespeed of rotation of which is highly variable).

The appended drawing comprises:

Figure l, a diagram of an example of embodiment of the invention.

Figures 2 to 10 which are reproductions of curves obtained on thechecking device of Figure 1 during the checking of an automobileinternal combustion engine.

Referring to Figure 1, it will be seen that the device comprises acathode ray tube 1 electrically supplied in any suitable manner asregards the heating circuits, etc. and comprising sets of deflectingplates 2 and 3 ensuring, respectively the horizontal and verticalscannings.

The vertical scanning 3 is connected with point B to which are connectedthrough the key 4, the spark plug, the coil, or any other element to bechecked. The calibrated potentiometer 5 is interposed for adjusting thecurve to a suitable height and for allowing, by means of a suitablecalibrating, a measurement of the voltage value of the pulse which isbeing checked.

The horizontal scanning 2 is connected with point E through the assemblyof two triodes 6 and 7 and of the change over 8 making it possible todirect the pulse to the grid of one or the other of the tubes 6, 7,according to its polarity, large resistances being interposed for thedouble purpose, on the one hand, of not damping too much the circuitfrom which the pulse is derived, so as not to modify the phenomenon tobe checked (for instance not to modify the spark between the electrodesof the spark plug to be checked) and on the other hand to cut down thevoltage applied to the grids to suitable values.

The change over 8 can be replaced by any suitable device either todirect the pulse to the suitable grid in accordance to its polarity orto transmit pulses having always the same polarity, whatever thepolarity of the pulses received may be.

According to this it is possible to use a double diode, rectifiers, etc.

The grid of tube 6 is normally negative, as results from its connectionon the bridge RiRz. The grid of tube 7 is normally positive, as resultsfrom its connection on the bridge R3R4. In the absence of anyphenomenon, the triode 6 therefore, is locked, the voltage on its plateis the power supply voltage, say +400 v. for instance and the triode 7passes current, its grid being positively biassed; the plate voltagewill depend on the resistances R5 and R7 and will be, for instance 25volts. The grid voltage of the triode 7 is applied to the tube cathodethrough a capacity.

The device operates as follows:

If a positive pulse P is connected at E, the change over being arrangedfor directing it to the triode 6, the grid of this tube becomes suddenlypositive, the equilibrium is upset, the tube is conducting and the platevoltage drops suddenly. This voltage drop is transmitted to the. Thegrid.

grid of the tube 7 through acondenser C1. of the tube 7 thus becomesnegative and the tube 7 is locked; the plate voltage on the tube 7increases suddenly and reinforces the positive voltage of the grid ofthe tube 6 for the duration of the time constant of the circuit RaCr.This set of operations has the result:

(a) Of generating a saw tooth voltage S in the scanning circuit, thecircuit R9C1 of which sets the duration independently of thepeculiarities of the pulse proper.

(b) Of causing a voltage drop on the cathode of the tube 7, which givesa square top wave having the effect of causing the emission of electronsin the cathode ray tube andconsequently the luminosity on the screen forthe duration of the pulse since it causes a negative pulse on thecathode.

As, on the other hand, the pulse to be studied is sent to the verticaldeflecting plates, the phenomenon is recorded on the, oscillograph witha complete synchronism between the two sjcannings, whatever maybe thefrequency of repetition of the pulse,- a frequency which may thus bevariable.

After this discharge period, the condenser Ci recharges through theresistance R9, the tube- 7 is unlocked and the initial equilibrium'isrestored; if the pulse is negative it will be sent to the grid of tube7lby a suitable switching ofthe change over 8. This grid becomingnegative, the tube 7 will be locked and its plate voltage will risesuddenly, supplying to the grid of lamp 6 a sudden posi-' tive voltagewhich makes this tube conducting and the rocess is re eated as in theprevious case.

It will be obvious that other electronic circuit may ive the sameresult; in particular, the two triode tubes 6 and 7 may be replaced by adouble triode or by two pentodes; other types of discharge tubesrnay beused (thyratron) the invention still consisting in starting theirdischarge by the pulse itself. The appended drawing represents aparticular and preferred embodiment of the invention, not limitativehowever.

The connecting of the apparatus on the element to be checked is effectedat point B by any suitable means such as a plug or mouth 4 with aninterposition of any suitable resistance, a ground connection of thebody consisting, in the case of an internal combustion engine, inconnecting the body of the motor to'the body of the checkingoscillograph, being also provided. 7

Figures 2 to l( are typical pictures of the curves obtained whenchecking the ignition of an internal combustion engine with a deviceaccording to the invention.

Figure 2 is the curve obtained with a normal ignition circuit; taken atthe terminals of thelspark plug giving sparks. V

Figure 3 is the curve obtained with a normal ignition circuit taken onthe spark plug Wire, the spark plug being disconnected (no spark).

Figure 4 shows a fouled spark plug, the ignition taking place however,the curve being also derived from the terminals of the spark plug.

The curve of Figure 6 means: a condenser fault, with no spark obtained,either no spark actually occurring or' ductive; means for positivelybiasing the control electrode of said second device so that said seconddevice is normally conductive; means for coupling the anodes of each ofsaid devices to the control electrodes of each of the other devices,respectively; a cathode ray tube having a pair of horizontal deflectingplates and a pair of vertical deflecting plates; means for applying thepulse to be tested to the control electrode of one of said deviceswhereby. this device reverses its'conductive state and emits an impulsethrough said coupling means to reverse the conductive state of the otherdevice; means for connecting the anode of the normally conducting'dcviceto said pair of horizontal defiecting'plates; and means included in saidtrigger circuit for synchronizing the emission of electrons in saidcathode ray tube with the application of said pulse to be tested.

2. A pulse testing apparatus comprising, in combination, a triggercircuit having a first and a second triode; power supply means forsupplying operating potentials for said triode's; means for negativelybiasing the control elec-.

trade of said first triode so thatlsaid first triode is normallynon-conductive; means for positively biasing the control electrode ofsaid second triode sothat said second triode, is normally conductive;means for coupling ,the V anodes of each of said triodes to the controlelectrodes of each of the other triodes, respectively; a cathode raytube having a pair of horizontal deflecting plates and a pair ofvertical deflecting plates; means for applying the pulse to be tested tothe control electrode of one of said triodes whereby this triodereverses its conductive state and emits an impulse through said couplingmeans to reverse the conductive state of the other triode; means forconnecting the anode of the normally conducting triode to said pair ofhorizontal deflecting plates; means for applying the trode of the firsthalf of said twin triode so that'said first the curve being taken on thespark plug wire the latter The curve in Figure 10 means that the coil isdefective (curve taken at the coil).

These curves show conclusively the interest of the device which makes itpossible to detect immediately the existence of a fault, its nature andorigin.

The apparatus, obviously, is not limited to its application to thechecking of internal combustion engines, any suitable apparatuscomprising an electric circuit in which regular shaped pulses arerepeated may be checked in an identical manner.

I claim:

1. A pulse testingapparatus comprising, in combination, a triggercircuit having a first and a second electron discharge device, each of.said devices having at least a cathode, an anode and a controlelectrode; power supply half is normally non-conducting;'means forpositively biasing the control electrode of the second half of said twintriode so that said second half is normally conductive; means forcoupling the anodes of each half of said twin triode to the controlelectrode of the other half respec V tivelyja cathode ray tube having apair of horizontal deflecting plates and a pair of verticaldeflectingplates;

means for applying the pulse to be tested to-the control ing the pulseto be tested to said pair of vertical deflecting plates; and meansincluded in said .trigger circuit for synchronizing the emission ofelectrons in said cathode ray tube with the application of said pulse tobe tested.

4. A pulse testing apparatus comprising, in combina-' tion, a triggercircuit having a first and a second electron discharge device, each ofsaid devices having at least a cathode, an anode and a controlelectrode; power supply means for supplying operating potentials for.said device, said operating potentials including a ground potential forsaid cathodes; mcanslfor negatively biasing the control electrode ofsaid firstdevice so that said first device isnorm'ally non-conductive; acapacitor connected be tween the anode of said. first device and thecontrol electrode of saidsecond device; a first resistor connectedbetween said control electrode and ground potential; a sec- 0nd resistorconnected between the anode of said second device and the controlelectrode of said first device; av

cathode ray tube having a pair of horizontal deflecting plates and apair of vertical deflecting plates; means for applying the pulse to betested to the control electrode of one of said devices whereby thisdevice reverses its conductive state and emits an impulse through saidcoupling means to reverse the conductive state of the other device;means for connecting the anode of the normally conducting device to saidpair of horizontal deflecting plates; means for applying the pulse to betested to said pair of vertical deflecting plates; and means included insaid trigger circuit for synchronizing the emission of electrons in saidcathode ray tube with the application of said pulse to be tested.

5. A pulse testing apparatus comprising, in combination, a triggercircuit having a first and a second electron discharge device, each ofsaid devices having at least a cathode, an anode and a controlelectrode; power supply means for supplying operating potentials forsaid devices; means for negatively biasing the control electrode of saidfirst device so that said first device is normally nonconductive; meansfor positively biasing the control electrode of said second device sothat said second device is normally conductive; means for coupling theanodes of each of said devices to the control electrodes of each of theother devices, respectively; a cathode ray tube having a pair ofhorizontal deflecting plates, a pair of vertical deflecting plates, anda cathode; means for applying the pulse to be tested to the controlelectrode of one of said devices whereby this device reverses itsconductive state and emits an impulse through said coupling means toreverse the conductive state of the other device; means for connectingthe anode of the normally conducting device to said pair of horizontaldeflecting plates; means for applying the pulse to be tested to saidpair of vertical deflecting plates; and means for connecting the cathodeof said second device to the cathode of said cathode ray tube forsynchronizing the emission of electrons in said cathode ray tube withthe application of said pulse to be tested.

6. A pulse testing apparatus comprising, in combination, a triggercircuit having a first and a second electron discharge device, each ofsaid devices having at least a cathode, an anode and a controlelectrode; power supply means for supplying operating potentials forsaid devices; means for negatively biasing the control electrode of saidfirst device so that said first device is normally nonconductive; meansfor positively biasing the control electrode of said second device sothat said second device is normally conductive; means for coupling theanodes of each of said devices to the control electrodes of each of theother devices, respectively; a cathode ray tube having a pair ofdeflecting plates and a pair of vertical deflecting plates; means forapplying a positive pulse to be tested to the control electrode of saidfirst device whereby this device starts to conduct and emits a negativeimpulse through said coupling means to block conduction of said seconddevice; means for connecting the anode of the normally conducting deviceto said pair of horizontal deflecting plates; means for applying thepulse to be tested to said pair of vertical deflecting plates; and meansincluded in said trigger circuit for synchronizing the emission ofelectrons in said cathode ray tube with the application of said pulse tobe tested.

7. A pulse testing apparatus comprising, in combination, a triggercircuit having a first and a second electron discharge device, each ofsaid devices having a least a cathode, an anode and a control electrode;power supply means for supplying operating potentials for said devices;means for negatively biasing the control electrode of said first deviceso that said first device is normally non-conductive; means forpositively biasing the control electrode of said second device so thatsaid second device is normally conductive; means for coupling the anodesof each of said devices to the control electrodes of each of the otherdevices, respectively; a cathode ray tube having a pair of horizontaldeflecting plates and a pair of vertical deflecting plates; means forapplying a negative pulse to be tested to the control electrode of saidsecond device whereby this device becomes non-conductive and emits apositive impulse through said coupling means to initiate conduction insaid first device; means for connecting the anode of the normallyconducting device to said pair of horizontal deflecting plates; andmeans included in said trigger circuit for synchronizing the emission ofelectrons in said cathode ray tube with the application of said pulse tobe tested.

8. A pulse testing apparatus comprising, in combination, a triggercircuit having a first and second electron discharge device, each ofsaid devices having at least a cathode, an anode and a controlelectrode; a power supply means for supplying operating potentials forsaid devices, said operating potentials including a ground potential forsaid cathodes; means for negatively biasing the control electrode ofsaid first device so that said first device is normally non-conductive;means for positively biasing the control electrode of said second deviceso that said second device is normally conductive; a capacitor connectedbetween the anode of said first device and the control electrode of saidsecond device; a first resistor connected between said control electrodeand ground potential; a second resistor connected between the anode ofsaid second device and the control electrode of said first device; acathode ray tube having a pair of horizontal deflecting plates, a pairof vertical deflecting plates, and a cathode; means for applying thepulse to be tested to the control electrode of one of said deviceswhereby this device reverses its conductive state and emits an impulsethrough said coupling means to reverse the conductive state of the otherdevice; means for connecting the anode of the normally conductive deviceto said pair of horizontal deflecting plates; means for applying thepulse to be tested to said pair of vertical deflecting plates; and meansfor connecting the cathode of said second device to the cathode of saidcathode ray tube for synchronizing the emission of electrons in saidcathode ray tube with the application of said pulse to be tested.

References Cited in the file of this patent UNITED STATES PATENTS2,373,145 Sensiper et al Apr. 10, 1945 2,402,168 Lifschutz June 18, 19462,414,323 Moe Jan. 14, 1947 2,420,516 Bischolf May 13, 1947 2,455,283Valley Nov. 30, 1948 2,477,615 Isbister Aug. 2, 1949

